REDUCTION BY CO-CO2 AND CRACKING OF IRON-ORE SINTERS .3. INFLUENCE OF SOME MINOR CONSTITUENTS

This investigation mainly deals with a synthetic iron ore sinter, but it has been checked that most observations are qualitatively of worth for an industrial sinter. These materials have been reduced by CO/CO2, conditions in which magnetite is the final iron oxide. Potassium has been added by evaporation of a K2CO3 solution on the sinter particles; sulphur has been introduced as COS in the gas (200 vpm); water vapour has been injected into the gas (at pH(2)O = 0.77, 4.6 and 11 Torr). Potassium enhances the reduction from 600 to 900°C (for the synthetic sinter). It is proposed to consider that it decreases the energy barrier due to bands bending at hematite surface. Sulphur inhibits the reduction at low temperatures, but has no effect at 600°C and above, as if its action involved a high energy barrier implying a strong temperature influence. Water vapour strongly decreases the induction period and significantly reduces cracking. This is interpreted by the interaction with the lattice dislocations inducing a softening of hematite. On the whole, the above-mentioned observations are very similar to what has been previously reported on the action of the same additives in the reduction of natural hematite crystals.